1. Field of the Invention
This invention relates to a recording liquid particularly suitable for an ink jet printer and a method for ink jet recording by allowing a recording liquid to fly from the orifices of a recording head by an action of heat energy.
2. Related Background Art
The ink jet recording system has such advantages as less generation of noises during the recording, easy response to colorization and high speed recording of images with a high resolution owing to the use of a highly integrated head. In the ink jet recording system, solutions of various water-soluble dyes in water or a mixture of water with an organic solvent have been used as inks. However, the water-soluble dyes themselves are poor in lightfastness, and thus the lightfastness of recorded images has been a problem in many cases. Furthermore, the waterfastness of recorded images has been also a problem in many cases due to the water solubility of the dyes. That is, recorded images are sometimes blurred or disappear when wetted with rain or sweat or splashed with water.
On the other hand, writing materials using a dye, such as ball-point pens, etc. have a similar problem, and in order to solve the problems of lightfastness and waterfastness, various aqueous pigment inks have been proposed for the writing materials. For practical applications of aqueous pigment inks, dispersion stability, prevention of inks from solidification at the tip of a pen, and prevention of balls of ball point pens from wearing have been investigated. For example, Japanese Patent Application Kokai (Laid-open) No. 61-246271 discloses an ink composition for writing materials with improved dispersion stability and drying resistance by using a water-soluble amine salt, ammonium salt or metal salt of copolymers comprising a hydrophilic, addition-polymerizable monomer and styrene and/or styrene derivative monomer as a water-soluble resin, and Japanese Patent Application Kokai (Laid-open) No. 62-72774 discloses an aqueous pigment ink free from an ejection-down phenomenon and an ink runout phenomenon by using polysiloxane.
When a conventional pigment ink using carbon black is used in the ink jet recording, the fastness of a printed product can be considerably improved, as compared with those when a dye ink is used, as mentioned above, but it was found by the successive investigation that there was such an inconvenience that the optical density of the printed product obtained with carbon black as one of characteristics of ink jet recording was inferior to that of the printed product obtained with a dye ink. In order to increase the optical density of printed products, it would have been taken into consideration to increase the concentration of pigment, but a pigment ink of high concentration had such a disadvantage as causing a serious trouble in the ejection stability. Furthermore, in the application of such a dispersion system as a pigment ink to the ink jet recording, prevention of the ink from solidification at the head tip end when left standing for a prolonged time was an important technical task and the ink composition was an important point in designing of reliable pigment inks.
Still furthermore, some of the conventional pigment inks had such problems as unstable ejection or ultimately a failure to discharge when the driving conditions for a recording head were changed or when the ink was continuously ejected for a long time, though it had good ejection characteristics for a relatively short time.